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Digital archive of theses discussed at the University of Pisa


Thesis etd-04032017-110826

Thesis type
Tesi di dottorato di ricerca
Thesis title
Iodine Intake, Thyroid Function and Pregnancy Outcome in a Tuscan Cohort of Women Living in an Area with Moderate Iodine Deficiency
Academic discipline
Course of study
tutor Prof. Tonacchera, Massimo
  • Gravidanza
  • Iodio
  • Tiroide
Graduation session start date
Thyroid hormones are crucial for fetal development. Pregnancy leads to multiple changes in thyroid function.
Aim of the study was to evaluate iodine intake, thyroid function and thyroid autoimmunity impact on pregnancy outcome.
Thyroid function, anti-thyroid antibodies, thyroid ultrasound, urinary iodine [UI], and pregnancy complications were analyzed at 10th, 15th, 20th, 25th and 35th weeks of pregnancy and 3-6 months after delivery in 902 women living in Tuscany, an area of moderate iodine deficiency.
Chronic autoimmune thyroiditis [CAT] was found in 414 women (45.9%). Of these, only 261 (63%) were aware of their disease before our evaluation. Similarly, a nodular disease was found in 138 women (15.3%), but only 89 (64%) knew about that before pregnancy.
At the first evaluation, iodized salt alone [S] was assumed by 31% of women, multivitamins containing iodine [M] by 20%, both [B] by 24% and none [N] by 25%. While a significantly higher UI and a higher number of women with UI over the desirable 150 µg/L value was measured in M and B groups, median UI was below 150 µg/L in all groups, both considering all women and only women not assuming any thyroid therapy.
A significant correlation between FT4, FT3 or TSH and UI was not found in either healthy women or women affected by a thyroid disease, but women with UI below 50 µg/L had a significantly lower FT3/FT4 ratio.
Thyroid volume significantly increased throughout pregnancy, this increase depending on both TSH and UI.
In women affected by autoimmune thyroiditis, both anti-thyroglobulin and anti-thyroperoxidase antibodies decreased during pregnancy and rebounded 3 months after delivery.
Analyzing the previous pregnancy history of recruited women (n=492 pregnancies), a miscarriage was reported in 51.4% of cases, without differences between healthy women and women affected by CAT (miscarriage prevalence being 53.9% and 49.9% respectively). No difference between women affected by CAT and healthy ones was found when considering the 902 pregnancies included in this study, although the prevalence in both groups was about 10%.
LT4 dose in women already treated at the beginning of pregnancy required an increase in 57% of women under suppressive therapy (mean increase 52%), 72% of women with autoimmune hypothyroidism (mean increase 33%) and 92% of thyroidectomized women (mean increase 34%). Moreover, 50 women affected by CAT and 5 with thyroid nodules initiated LT4 therapy during pregnancy, mean final dose being 64.2±31.1 µg/die and 55.0±27.4 µg/die respectively.
In conclusion, almost a half of women affected by a thyroid disease were not aware of their disease at the beginning of pregnancy, suggesting that a universal screening could be useful. While S seems to be not enough a supplementation during pregnancy, M are able to increase UI but the majority of women continue to have an insufficient iodine uptake. Moreover, M are assumed by a minority of women, suggesting an improvement in supplementation programs is needed. This is crucial when considering that FT3/FT4 ratio increased in women with very low UI, suggesting a role of UI in isolated hypothyroxinemia, which has been previously correlated with children cognitive abilities. While an increase in LT4 therapy is often required, this is not true for all women and varies in different thyroid diseases, so that any change in the dose should follow an early, frequent and personalized thyroid function evaluation.